<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        html{height: 100%}
        body{margin: 0;height: 100%;
            background: #fff;}
        canvas{display: block;width: 100%;height: 100%;}
        .body_content{
            position: absolute;
            top:30%;
            left: 20%;
            height: 20%;
            background: palevioletred;
            width: 20%;
        }
    </style>
</head>
<body>
<canvas id="canvas"></canvas>
<script src="index.js"></script>


</body>
</html>